1. Field of the Invention
This invention relates to a suspension device for automobile in which characteristic of the suspension device is changed over by changing pressure of a fluid depending on cruising condition of an automobile or preferance of a driver.
2. Discussion of the Background
There is contradiction between the characteristic of the suspension device, e.g., damping factor characteristic of a shock absorber and spring characteristic of a suspension spring, when comfortableness in vehicle riding is considered to be serious and those of the suspension device when steering stability is considered to be serious. Accordingly, it is difficult to simultaneously satisfy both the characteristics. However, recent development of electronics allows various proposals of systems in which characteristic of a suspension device is changed over depending on necessity. Generally, there have been known methods of changing over the characteristic of the suspension device as follows. For changing over the damping force of a shock absorber, a rod arranged at the central portion of the shock absorber is rotated so that the diameter of an orifice is changed to be large or small. For changing over the spring characteristic of a spring for suspending a vehicle body, connecting paths of a plurality of air chambers provided in the suspension device are communicated or interrupted by turning movement of a central rod to thereby change over a spring constant. Thus, changing-over of the characteristic of the suspension device is realized by turning the rod. There is a proposal of a suspension device in which a rotary solenoid having direct connection to an end of the rod is used as an actuator for rotating the rod. A suspension device provided with a rotary solenoid as an actuator has, however, such drawback that the structure of the solenoid is complicated; large stroke can not be obtained and force for rotating the rod is weak and that it is difficult to miniaturize the actuator which is essential to reduce a space for installation.